Over the years, body characteristics have been determined by obtaining a sample of bodily fluid. For example, diabetics often test for blood glucose levels. Traditional blood glucose determinations have utilized a finger prick using a lancet to withdraw a small blood sample. These systems are designed to provide data at discrete points and do not provide continuous data to show the variations in the characteristic between testing times. These discrete measurements are good to give some idea on how one's blood glucose values are at a point in time, and thus, enough information for a diabetic to give “correction” amounts of insulin to reduce their current blood glucose reading. However, these discrete readings are not able to provide enough information for any type of automatic or semi-automatic system of giving insulin based on blood glucose values.
Recently, a variety of implantable electrochemical sensors have been developed for detecting and/or quantifying specific agents or compositions in a patient's blood or interstitial fluid. For instance, glucose sensors are being developed for use in obtaining an indication of blood glucose levels in a diabetic patient. These glucose sensors connected (wired or wirelessly) to a blood glucose monitor can provide continuous glucose readings over a period of time such as 3 to 5 days. Such readings are useful in monitoring and/or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient. Thus, blood glucose readings improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which are herein incorporated by reference. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated by reference herein. See also U.S. Pat. No. 5,299,571. In addition, characteristic glucose monitors used to provide continuous glucose data are described in commonly assigned U.S. patent application Ser. No. 11/322,568 entitled “Telemetered Characteristic Monitor System and Method of Using the Same” filed on Dec. 30, 2005, which is herein incorporated by reference in its entirety. In addition, infusion pumps receiving sensor data is described in commonly assigned U.S. patent application Ser. No. 10/867,529 entitled “System for Providing Blood Glucose Measurements to an Infusion Device” filed on Oct. 14, 2004, which is herein incorporated by reference in its entirety.
As sensor technology improves, there is greater desire to use the sensor values to control the infusion of drugs and medicine, like insulin in a closed loop or semi-closed loop system. Specifically, a closed loop system for diabetes would entail a glucose sensor and an insulin infusion pump attached to a patient, where the delivery of insulin would be automatically administered by the controller of the infusion pump based on the sensor's glucose value readings. A semi-closed system would typically include a patient intervention step where the amount of insulin to be infused as calculated by the controller of the infusion pump would require a patient acceptance before delivery. However, given the ramifications of over-delivery and/or under delivery of medication, no one has yet to develop a viable way to actually create a working closed loop/semi-closed loop system where obtained sensor values can be trusted enough to be used to control the delivery of medication such as insulin with sufficient safeguards to operate on its own or even with a patient confirm/decline step.